Thrust reverser comprising optimized deflector gratings

ABSTRACT

The invention relates to a device comprising gratings, which are used to form a reverse flow from a jet engine thrust flow. The inventive device comprises a plurality of flow diverter gratings which are disposed side-by-side at the outer edge of an annular thrust flow circulation channel. Each of the gratings comprises a plurality of intersecting inner transverse blades and inner longitudinal blades, two adjacent gratings being separated by a side clearance which generates a leakage flow. The device also comprises means of re-directing the aforementioned leakage flow in a direction such as to increase the effectiveness of the reverse flow, said re-direction means comprising aerodynamic appendages which are mounted to at least one outer longitudinal edge of each grating.

FIELD OF THE INVENTION

The present invention relates to thrust-reversal devices for bypassturbojet engines and relates more specifically to an improvement to theflow deflection cascades also known as gratings used inside suchdevices.

PRIOR ART

Conventionally, a bypass turbojet engine is equipped with a passagebehind the fan and whose purpose is to channel the so-called coldsecondary flow. This passage is made up of an internal wall surroundingthe structure of the actual engine behind the fan, and of an externalwall the upstream part of which is a continuation of the engine casingwhich surrounds this fan. This external wall can channel both thesecondary flow and the primary flow in its downstream part, this beingbehind the ejection of the so-called hot primary flow in the case ofmixed-flow nacelles or confluent-flow nacelles for example. By contrast,in the case of so-called separate-flow nacelles, the external wallchannels only the secondary flow.

One wall may also streamline the outside of the engine, that is to saythe outside of the casing surrounding the fan and the outside of theexterior wall of the aforementioned passage, this being with a view tominimizing the drag of the propulsion unit, particularly in the case ofpropulsion units attached to the outside of the aircraft, such as thoseattached on or under the wings or at the rear of the fuselage forexample.

FIGS. 1 to 3 illustrate a known exemplary embodiment of a thrustreverser with deflection cascades applied to a bypass turbojet engine.

Such a turbojet engine thrust reverser 10 comprises a moving cowling 12,advantageously made up of two cylindrical half-parts and forming, whenthe turbojet engine is operating in direct thrust mode, all or part ofthe downstream end of the external wall of the annular duct 14 throughwhich the stream of secondary flow circulates, and able to be movedaxially in the downstream direction by means of an operating system (notdepicted) comprising, for example, jacks fixed to the upstream part ofthe reverser. Moving the cowling in the downstream direction causes thepivoting of a plurality of flaps 16 via link rods 18 connected to apoint of articulation on the internal wall 20 of the annular duct 14,these flaps closing off the duct and deflecting the flow in order toform a reversal flow which is guided by means of a cascade device 22arranged on the external periphery of this duct and of which thecascades, mounted side by side, are uncovered once the cowling has beenmoved in the downstream direction. These cascades comprise vane setswith greater or less curvature, in one or two directions, depending onthe direction desired for the reversal thrust. Specifically, whenreversing the thrust, it is necessary to direct the flow passing throughcertain cascades of the device in a given direction in order to preventthe air from striking undesired parts of the airplane and to avoiddirect contact with the ground, in order to minimize or even cancel thepossibility that the engine that generates this flow or a nearby enginemight ingest this air by ricochet. This special orientation of the setsof vanes also avoids driving any obstacle present on the tarmac ontostructures of the airplane, through the same ricochet phenomenon.

In the cascade device illustrated, each cascade is mounted in aparallelepipedal surround in order, on the one hand, to make it easierto install and to fit back on the structure of the nacelle, particularlyduring maintenance operations where the intervention time is of verygreat importance and therefore has to be as short as possible and, onthe other hand, to give the reversal flow better aerodynamic propertiesbecause the width for the passage of the air needs to be approximatelythe same at the inlet and at the outlet, in the thickness of thecascade. To this end, the aerodynamic configuration of the transversevanes 24A (longitudinal vanes 24B being straight) of the cascades isdesigned in such a way as to convert the thrust flow passing throughthem into a reversal flow advantageously directed toward the front ofthe nacelle.

Each cascade is fixed to the structure of the nacelle in theconventional way by screws 23 passing, on the one hand, through a fronttransverse edge 22A and screwed into a structural front part 26 of thereverser and, on the other hand, through a transverse rear edge 22B andfixed into a rear structural part 28 of this reverser. By contrast, theadjacent or middle cascades are not joined together via their parallellongitudinal edges 22C and there is therefore a lateral clearance 30between each of the cascades of the thrust reverser cascade device.

Bearing in mind the manufacturing installation tolerances, thisclearance may prove to be large enough that it generates an air leak 32in a vertical direction, or even one directed toward the rear of thenacelle, of a particularly great magnitude when the thrust is beingreversed, and which then reduces the effectiveness of the two reversalflows 34 leaving the cascades directly on each side of this leak 32,thus producing a thrust towards the rear of the nacelle that is likelyto greatly reduce the performance of the aerodynamic braking of theairplane.

This leakage phenomenon is aggravated with a configuration of cascadeswhich have their outlet toward the side, as illustrated in FIG. 4, andin which, depending on the desired direction of flow reversal, thelongitudinal vanes 24B of these cascades are curved to a greater orlesser extent in one same direction.

In this configuration, the clearance 31 is greater than the clearancethat corresponds to a cascade of parallelepipedal base (the example ofFIG. 3) and the negative effect of the leakage flow 32 on the reversalflows directly in contact with it is therefore amplified. To compensatefor this negative effect, a conventional approach is to have a far moreclosed angular arrangement of the transverse vanes 24A and, if need be,of the longitudinal vanes 24B towards the front of the nacelle,necessitating an increase in the length of the cascades in order forthem to retain the same cross-sectional area for the passage of the air,something which entails increasing the mass of numerous components,particularly the jacks, thereby affecting the reliability of theseparts.

OBJECT AND SUBJECT OF THE INVENTION

The subject of the invention is a deflection cascade device whichalleviates these drawbacks. An object of the invention is also toprovide a thrust reverser which offers ease of installation and ofre-fitting or maintenance of all components of the nacelle, particularlythe cascades. In effect, depending on the position of the nacelle on thewings of the airplane, for example in the case of a four-enginedairplane, the configuration of the reversal flow may differ from onenacelle to another. This means providing a panoply of cascades withdifferent vane configurations but which can be adapted and interchangedwith one another.

These objects are achieved by a cascade device having a reversed flowfrom the thrust flow of a turbojet engine, comprising a plurality offlow deflection cascades arranged side by side at the external peripheryof an annular duct for the circulation of the thrust flow, each cascadeconsisting of a plurality of transverse internal vanes and longitudinalinternal vanes crossing one another, two adjacent cascades beingseparated by a lateral clearance that generates a leakage flow,characterized in that it comprises means for re-directing said leakageflow in a direction that increases the effectiveness of said reversalflow.

Thus, the leaks are limited and the flow leaving the cascades isre-directed in the desired direction.

Advantageously, the means for re-directing the leakage flow compriseaerodynamic appendages mounted on at least or on the two longitudinalexternal edges of each cascade, said longitudinal external edge of thecascade preferably consisting of a longitudinal vane.

As a preference, said aerodynamic appendages comprise a plurality oftransverse vane tips and each vane tip of said plurality of transversevane tips of a given cascade has a curvature the same as or differentfrom that of the transverse internal vanes of said cascade. Each vanetip of said plurality of transverse vane tips of a given cascade may bearranged in the continuation of the transverse internal vanes of saidcascade and said plurality of transverse vane tips may be arranged in adifferent number by comparison with the transverse internal vanes of onesame cascade.

According to an advantageous embodiment, the number and the curvature ofsaid plurality of transverse vane tips are identical for all thecascades of the device regardless of the number and curvature of thetransverse internal vanes. Thus, it is possible to fit aerodynamicappendages to the outside of the longitudinal curved vanes inside theparallelepipedal initial envelope and allow any configuration ofcascades with respect to each other to be installed.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will be better understoodfrom reading the description which will follow of some preferredembodiments of the invention, with reference to the attached drawings inwhich:

FIG. 1 depicts a schematic half-view, in longitudinal section, of athrust reverser with deflection cascades according to the prior art,depicted in the closed position,

FIG. 2 depicts a schematic half-view, in section along the plane of thecascades, of the thrust reverser of FIG. 1.

FIG. 3 depicts a magnification of a detail of FIG. 2, illustrating themiddle arrangement of the deflection cascades,

FIG. 4 depicts an arrangement similar to that of FIG. 3, applied to avariant of the prior art,

FIG. 5A depicts a schematic half-view, in longitudinal section, of athrust reverser with deflection cascades according to a first exemplaryembodiment of the invention, depicted in the semi-open position,

FIG. 5B illustrates a partial view from above of the thrust reverser ofFIG. 5A, restricted to its cascades device,

FIG. 5C depicts an arrangement similar to that of FIG. 3, applied to thefirst exemplary embodiment of the invention of FIGS. 5A and 5B,

FIG. 6 depicts an arrangement similar to that of FIG. 3 applied to asecond exemplary embodiment of the invention,

FIG. 7 depicts a magnified detail of an end part of a deflection cascadeillustrated in FIG. 6,

FIG. 8 depicts a lateral arrangement, in perspective, of two middlecascades according to the second exemplary embodiment of the invention,

FIG. 9 depicts, in perspective, a lateral arrangement of two middlecascades according to an alternative form of the second exemplaryembodiment of the invention, and

FIG. 10 depicts an arrangement similar to that of FIG. 3, applied to athird exemplary embodiment of the invention.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

A first exemplary embodiment of the invention applied to a thrustreverser with its outlet forward (that is to say in a direction oppositeto the airplane thrust direction) as illustrated in FIG. 5A to 5C. FIG.5A is a schematic half view, in longitudinal section, of a thrustreverser with deflection cascades the cowling of which is depicted inthe semi-open position. FIG. 5B is a partial view from above of thenacelle, cowling open, uncovering the cascades of the thrust reverserand FIG. 5C shows, in detail, the interface between two adjacent ormiddle cascades 22.

According to the invention, the cascade device comprises means forredirecting forward (in the direction of the reverse flow) the parasiticflow created by the air leak 32 and which was initially at best neutralor at worst generated thrust, so as to improve the effectiveness of thereverse flow. To do this, aerodynamic appendages in the form oftransverse vane tips 36 mounted on a longitudinal external edge 22C ofeach cascade 22 in order to fill the space resulting from the circularlayout of the cascade device are added. Each cascade conventionallyconsists of a plurality of transverse internal vanes 24A and oflongitudinal internal vanes 24B which cross one another. Also, theseadditional appendages are advantageously arranged in the continuation ofthe transverse vanes 24A and each has a curvature identical to that ofthe transverse vanes. Thus, the leak is immediately taken in hand by thevane tips which then, like the transverse vanes, direct it towards thefront of the nacelle. However, this configuration is not compulsory andthe vane tips 36 may be arranged differently, that is to say may be notaligned with the transverse vanes. The number of vane tips may alsodiffer from the total number of transverse vanes. The curvature of thesevane tips may differ from that of the transverse vanes. Finally, eachvane tip may have a different configuration from its neighbor andlikewise for each spacing. Furthermore, this addition of vane tips givesthe cascades a trapezoidal cross section by comparison with theirinitial rectangular cross section, thus increasing the-total surfacearea for the passage of air through these cascades.

FIG. 6 is a view depicting a section along the axis of the nacellethrough a plane passing through the cascades of a thrust reversal devicewith its outlet to the side (that is to say in a direction at rightangles to the direction of thrust of the airplane).

In this configuration, the cascade device comprises means forredirecting, in the direction of the reversal flow, the parasitic flowcreated by the air leak 32. These means comprise transverse vane tips36, 38 fixed to the two longitudinal external edges 22C of each cascade22 so as to fill the space created by the initial longitudinal clearance31 resulting from the curvatures of the transverse vanes 24B. Thelongitudinal cutout of the vane tips 36, 38 is no longer parallel to anaxis 40 passing through the center 42 of the nacelle and the center ofthe cascade 22 but is now parallel to an axis 44 passing through thecenter 42 of the nacelle and the middle of the residual longitudinalclearance 46. The cascade 22 is thus in the form of a “trapezium-shape”configuration now rather than a parallelepiped shape, and this, likebefore, slightly increases the surface area for guiding the flow.

Two further advantages stem from this configuration. The first is aresidual leak 48 reduced to a magnitude comparable with a cascadeconfiguration in which the outlet is forward. The second is that thisresidual leak is immediately taken in hand by the vane tips which,through this effect, give it a direction parallel to the reversal flow,namely toward the front of the nacelle so that it is no longer neutralor a generator of thrust. The reversal flows 34 leaving the vanesdirectly at the middle of the leak 48 are thereby less disrupted. Thisresults in better effectiveness of the reversal assembly making itpossible to reduce the length of the cascades, for the sameeffectiveness, by comparison with the design in which the leaks were notmanaged. The mass of many components such as the jacks that operate themoving cowling is thereby reduced and the reliability of the system andof the components concerned is increased.

Furthermore, the detailed view of FIG. 7 shows the longitudinal vane 24Bin contact with the vane tip 38 enjoys the trapezoidal extension of theconfiguration of the cascade 22 and thus increases the total surfacearea for the passage of air through this cascade. The initial leakageregion is thus filled with appropriate appendages improving thedirection of the reversal flow passing through these leakage spaces.

FIG. 8 is a perspective depiction of the arrangement of two middlecascades as shown in FIG. 6 and 7. In this configuration, the transversevane tips 36, 38 are depicted in the continuation of the transversevanes 24A, also known as internal vanes. However, this arrangement ofthe vane tips is not compulsory because, in particular, each definitionof blading may differ from one cascade to another. Thus, as in theprevious embodiment, vane tips 36 may be not aligned with the vane tips38. Likewise, it may be noted that the definition of the vane tips 36,38 may be specific and different from the transverse vanes 24A of oneand the same cascade, in particular in terms of their shape, number andarrangement, these parameters being chosen by the person skilled in theart according to the desired effect.

FIG. 9 depicts a solution to this problem using a unique design for thetransverse vane tips 36, 38. Using this remarkable configuration, thevane tips 36 applied to absolutely any configuration of cascade alwaysfind themselves in register with the vane tips 38 of absolutely anyother configuration of cascade, ensuring optimum aerodynamic performanceof the leakage flow.

A second exemplary embodiment of the invention is illustrated in FIG.10. In effect, it is possible to imagine that, for a cascadeconfiguration that is identical for any reverser, the most suitablesolution would be to provide a single set of vane tips 50 which could bemounted on one or other side of the cascade 22 and dimensioned tocorrespond to the full width between two longitudinal vanes 24B of twomiddle cascades, give or take the mounting clearance and tolerances. Theoverall performance is thereby further enhanced with an appreciableimprovement in weight saving and reliability.

Furthermore, this arrangement may easily be applied to configurationsalready in operation without changing the structure of the surroundingcomponents. The gain would then be an appreciable improvement in thereversal performance or even, for the same sought-after reverserreversal effectiveness prior to fitting the panoply, the possibility ofusing the engine at a lower speed than the speed usually used, thusimproving engine life.

1. A cascade device having a reversed flow from the thrust flow of aturbojet engine, comprising a plurality of flow deflection cascadesarranged side by side at the external periphery of an annular duct forthe circulation of the thrust flow, each cascade consisting of aplurality of transverse internal vanes and longitudinal internal vanescrossing one another, two adjacent cascades being separated by a lateralclearance that generates a leakage flow, characterized in that thecascade device comprises means for re-directing said leakage flow in adirection that increases the effectiveness of said reversal flow.
 2. Thecascade device as claimed in claim 1, characterized in that said meansfor re-directing the leakage flow comprise aerodynamic appendagesmounted on at least one longitudinal external edge of each cascade. 3.The cascade device as claimed in claim 2, characterized in that theaerodynamic appendages are mounted on the two longitudinal externaledges of each cascade.
 4. The cascade device as claimed in claim 2,characterized in that said longitudinal external edge of the cascadeconsists of a longitudinal vane.
 5. The cascade device as claimed inclaim 2, characterized in that said aerodynamic appendages comprise aplurality of transverse vane tips.
 6. The cascade device as claimed inclaim 5, characterized in that each vane tip of said plurality oftransverse vane tips of a given cascade has a curvature identical tothat of the transverse internal vanes of said cascade.
 7. The cascadedevice as claimed in claim 5, characterized in that each vane tip ofsaid plurality of transverse vane tips of a given cascade has acurvature different from that of the transverse internal vanes of saidcascade.
 8. The cascade device as claimed in claim 5, characterized inthat each vane tip of said plurality of transverse vane tips of a givencascade is arranged in the continuation of the transverse internal vanesof said cascade.
 9. The cascade device as claimed in claim 5,characterized in that said plurality of transverse vane tips is set outin a different number by comparison with the transverse internal vanesof the same cascade.
 10. The cascade device as claimed in claim 5,characterized in that the number and curvature of said plurality oftransverse vane tips are identical for all the cascades of the deviceregardless of the number and curvature of the transverse internal vanes.11. A thrust reverser for a bypass turbojet engine comprising a cascadedevice as claimed in claim 1.